1. Field of the Invention
The present invention relates to an image pickup system capable of performing zoom tracking control by moving an image sensor, particularly to a lens-interchangeable image pickup system.
2. Description of the Related Art
Image-taking optical systems, which are capable of performing variation of magnification by moving a magnification-varying lens and in which the variation of magnification causes image plane variation, move a compensating lens (for example, a focus lens) other than the magnification-varying lens in an optical axis direction so as to compensate for the image plane variation to maintain an in-focus state. Control of such movement of the compensating lens for compensating for the image plane variation caused due to the variation of magnification is referred to as “zoom tracking (or zoom tracking control)”.
Japanese Patent Laid-Open No. 63-087871 discloses a camera that moves, in addition to the movement of the compensating lens, an image sensor, which photoelectrically converts an object image, in the optical axis direction to compensate for the image plane variation. Performing zoom tracking that moves the image sensor with the movement of the compensating lens enables reduction of a movable range required for the compensating lens, which makes it possible to miniaturize the camera.
However, in order to realize the zoom tracking by the movement of the image sensor in a lens-interchangeable image pickup system including a camera and an interchangeable lens to be attached thereto, the following problem should be solved. The problem is that, in a case where the camera performs the movement control of the image sensor according to the variation of magnification in the interchangeable lens, the camera should perform appropriate movement control of the image sensor according to an optical configuration and an optical characteristic of the interchangeable lens. Inappropriate movement control of the image sensor makes it impossible to obtain a good zoom tracking result.